Fuse



May 2, 1950 LUDWIG 2,506,304

FUSE

Filed Aug. 1, 1946 FIG.4

INVENTOR gay/Cr ,4 00/106" 5 TORNEY Patented May 2, 1950 UNITED STATES PATENT OFFICE FUSE Louis Ludwig, Brooklyn, N. Y.

Application August 1, 1946, Serial No. 687,677

3 Claims. 1

This invention relates to fuses.

It is an object of the invention to provide a fuse whose rupture is delayed upon the application of a slight overload current but which, when it blows under such an overload, makes a quick and positive break.

It is an other object of the invention to provide a fuse of the character described comprising relatively few and simple parts which can be manufactured at a low cost and assembled by comparatively unskilled help.

It is a further object of the invention to provide a fuse of the character described which is rugged and highly reliable in operation.

Other objects of the invention will, in part, be obvious and in part hereinafter pointed out.

The invention accordingly consists in the features of construction, combinations of elements and arrangements of parts which will be exemplified in the construction hereinafter described and of which the scope of application will be indicated in the appended claims.

In the accompanying drawings, in which is shown one of the various possible embodiments of the present invention:

Fig. l is a side elevational view of a fuse constructed in accordance with the invention;

Fig. 2 is a top plan view thereof with the cap off;

' Fig. 3 is a sectional view taken substantially along the line 3-3 in Fig. 2; and

Fig. 4 is an enlarged sectional view taken substantially along the line 44 in Fig. 3.

Referring now in detail to the figures, In denotes a fuse embodying my invention and comprising a conventional body l2 of porcelain or like insulating material, said body having an upwardly opening interior recess l3 which houses the active fuse elements. The body includes a flared upper rim l4 on which there is mounted a brass cap l6 whose skirt l8 envelopes the rim and is crimped in as at 20 to hold the cap in place. The crown of the cap is provided with a large central aperture 22 through which the recess can be seen. Said aperture is closed by a disc 24 of transparent material, such for example as mica, which is interposed between the crown and the rim l4 to protect the fuse elements without concealing them. An external integral helical ridge 26 on the body receives a threaded brass ferrule 28 whose lower edge has an inturned integral flange 20 abutting against an annular shoulder 32 near the bottom of the body. Said shoulder encircles a pendant pro- Jection 34 which is. centrally apertured toac- 2 commodate a hollow headed rivet 36 functioning as the bottom contact for the fuse plug.

An overly long fusible metal strip 38 extends from the bottom contact to the ferrule 28, being connected by a blob of solder 40 to the inside of the shank of the contact and by a blob of solder 42 to the interior of the ferrule. The strip passes through an opening 44 in the side of the body in order to make contact with the ferrule. If desired, fills 46, 48 of plaster of Paris or some other suitable mastic may be used to cover the soldered ends of the strip in order to improve the appearance of the plug and arrest the electric are before it reaches the contacts.

A portion 50 of the fusible strip is reduced in cross-section to constitute the fuse link. Said link has a cross-sectional area of predetermined size and shape such that the heat generated therein by a current in excess of a certain amount will fuse the link thereby causing an electric circuit to be interrupted.

As thus far described, the fuse plug is entirely conventional and has only been depicted in detail to afford a better understanding of my invention.

Pursuant to my invention I have provided means to somewhat delay the blowing (fusion) of the link, said means being designed to be of particular use when a slight overload is imposed, that is to say, said means should operate to prevent the link from blowing very shortly after the application of such an overload, thus extending the period of time over which the slight overload can be imposed. However, said means should not prevent the link from fusing immediately upon the application of a heavy overload caused, for instance, by a short circuit.

Furthermore, the fuse plug should, in accordance with my invention, incorporate means for quickly making a wide break between the fused ends of the link and interposing a solid dielectric therebetween when the link does blow, so that, despite the delayed incidence of the break under a slight overload, upon occurrence of the break either no arc will be formed or any are formed will quickly be quenched.

Moreover, both the foregoing means should be of such construction that they can be included in a standard fuse plug with the addition of but few and simple extra parts in order that the fuse may not become unduly complicated and its price unduly high.

As shown herein, the above means, i. e., the means for delaying the blowing of the link and for preventing or quenching the resultant arc,

comprises an element 52 made from a dielectric material, e. g. soapstone, having a high heat storage capacity and a high coefficient of thermal conductivity. Said element is semi-circular in cross-section and has a deep central groove 54 in its flat bottom surface running parallel to the axis of revolution of the curved upper surface of the element whereby the curved upper surface of said element is symmetrical with respect to the closed end of the groove. A shallow aarcuate groove 56 is provided in said curved upper surface, the same forming lateral rails 58, 60. The element 52 is supported by a wire bridge 62 of a resilient material, such for instance as steel or Phosphor bronze, which extends through the slot 54 and has its ends resting upon diametricallyopposite portions of an annularxinsetor :shelf 64 formed on the inside of the exterior recess l3 adjacent the upper edge thereof.

The groove 55 is slightly Wider than the strip 38 so said strip will: be. confined between; the. rails 58, (ill and, as-a result,.-.t'he element 52-wil1 be seeouredin definite relationship withrespect tomthc stripxuntilthezfusablows. :The element-.52 is::designed to :keep the 1-.strip under tension "by pressure. applied at theilmkdll and .for this purpose the length of-cthe overly long stripi38. is made. such 'that' when: said elementlies. underithe slackobend of zthe strip and; isamlged upwardly by the. spring wire. 62 it will .taire np all of. the slack while the spring is still bowedunderztension. as. indicated-by theisolid linesinsFig. 4. .LIl'liOlThflrWOIfidS,1311851101 maloperatingipositioniof the fusevelements'. seen in Figs. 3. andiezisisuchrthatlthe. fuse :strip is kept under tension zby npwardlipressureof ithe element 52:against;the linkifill arising: from bowingrof the Elli-11161 52. The :element. andxwine Jane; placed in thia 13.0511- tion :by first introdncing'ithe iiwire beneathithe the wire on the shel-fii. At.suchz-timautheWil a, which. has a slight zpreiormed nnrvature imparted thereto, adoes vnotccontact the fusible -;Sll1i'D. Thenthe elementdssetrastride the wire on one side of the fusible strip and is pressed dowznvlal'd- FJ-hen-:a;s"ght current nverload'is imposed on i therebyvkeeping cidoivn the temperature cf the fusible strip. xofzzcoursepafter the .passage of some. time bhQGElBIIlGIltfiEWfll itself Floeoomezhfiated to :quite tempcratureandwillsabsorb heat more-and snore :rslowlyiallowing itheulinkvto reach its fusion. temperature, avhereeupon ithegfuse emphasize'd zthat zas 211F115 -.e1eifusihle expand .ivhile ementnon'tinu- "onslyre go the 'lil'lk'lllfilfil" ithaibiasingzfiorce of the sprin nae zmaintainingigoodicontact betweenzthe strip.=and.elemont andiinsui'ingiexcellent :heat transferalcupto :time-;tl1at .the. strip :blows.

As soon as the fuse link 56 :melta the. dielectric zelementfzsf wi-llzbe sprung-upwardly by:the .wi1e.6 2 .to rapidly;parttthetwoiendsof;;the.rstrip formerly ings is to be interpreted as illustrative and not in 5a limiting sense.

Having thus described my invention, I claim as -newand-desire to secure by Letters Patent:

.1. .Alfuse.plugflcomprising a hollow dielectric body, a fusible elongated member housed in said bcdywith its ends fixedly supported at points spaced apart a distance less than the length of said member thereby; providingslack the member, said; member including :a portion :having a crossssectional area less than that of the '.-r.e.-. mainderof said member,.:a dielectric ..-element.of material, such :as soapstone,. having a 2 high heat storage capacity and ahigh coeiificientof thermal conductivity, said element :being .centrally disposed in .saidlbodyout of contact with the svallszthereof and having a curvedsurface baneath and in surface-contact with-:the portion of said member of lesser cross-sectional area, and an elongated-slender resilient normally straight wire having its ends unconfined and resting on shelves at opposite sides "ofsaidbody adjacent the top thereof, said =w-ire extending across the interior of said body and passing through an opening in saidelement,-said-wire being bowed under pressure-away from the top-ofsaid body so as to resiliently urge --saidelement toward said member whereby the heatgenerated in said member portion upon-the application of a-slight current overload will be absorbed bysaid element so as to delay the fusionof said'member.

2. A-fuse plugcomprising ahollow dielectric body, a fusible elongated member housed in said body with'its ends fixedly supportedat points spacedapart ;a distance less *thanthe lengthof said member thereby providing-slack-iu-the member, said member including a portion having-a cross-sectional area less thanthat of the remainder of said "member, a'dielectric'element of material, such as soapstone; having a high heat storage capacity and a high coefiicient of thermal conductivity, said element being centrally disposed in saidbody out.of contactwith the walls thereof and having a.symmetricallycurved,surface beneath and in surface contact with the portion of said member of lesser cross-sectional area and anie on ated slend resilient no mal y straight wirehavingitsends unconfine amn stin on shelves at on os tas de .Q sa dhqd adiacent the .top thereof, said wir ex endin p r lle to .the :axis ,of symmetry of .the. curved surface across the ,interiorof said body and passing through ,an-openingin saidtelemant, .said wire beingbowed -:und er ;press,ure ;away from .-the top of said-body so as to resiliently urge said clement towards id member Wh rcby th :he enerat d in ;said::member portinn upon the application of a slight current overload'will be absorbed tby said element so :as .tordelay theffusion. of Lsaidmember.

13. A fuse 'plugzcomprising adielectrict fuse'body having :':an mpwardly -opening interior srecess, a

ibridgedlby the link. .Said:element'thuswilrbe i-nx .threaded:electrically conductive shell aroundithe 5 side walls of said body, a central contact at the bottom of said body, a fusible electrically conductive elongated member in said recess, the ends of said member being permanently electrically connected to said bottom contact and said shell, a major portion of the length of said member being curved whereby to provide slack in the member within the recess, a soapstone element having a curved surface engaging the underside of said member, the underside of said element having a downwardly opening recess which extends from side to side of said element, an elongated slender resilient normally straight wire disposed in said recess and on which said element is supported, the ends of said wire being unconfined and resting on shelves on opposite sides of said body adjacent the top thereof, said wire being bowed under pressure away from the top of said body so as to resiliently urge said element against said member. whereby to delay the fusion of said member upon the application of a slight current overload and to quickly quench the are that may be formed when the fuse blows.

LOUIS LUDWIG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,061,894 Baker May 13, 1913 1,600,435 Strongson Sept. 21, 1926 2,129,309 Stewart Sept. 6, 1938 2,210,036 McEntee Aug. 6, 1940 2,234,020 Bussmann Mar. 4, 1941 2,303,661 Schmidt Dec. 1, 1942 OTHER REFERENCES Encyclopaedia Britannica, 11th edition, volume 26, page 369. 

